High temperature lubricant



Patented Sept. 2, 1947 STATES PATENT Donald L. Wright, Westfield, N. J., assignor to Jason, Incorporated, a corporation of Louisiana No Drawing. Application September 15, 1943, Serial No. 502,459

Claims.

This invention relates to a lubricating composition and to methods of lubrication, and more particularly to those suitable at high temperatures, especially at temperatures high enough to cause charring or varnish and tar formation with the lubricating oil compositions used heretofore.

On object of the invention is the lubrication of devices such as oven conveyor chains, wheel bearings of kiln cars, annealing oven cars, ejector pins and other hot moving parts of die-casting machines, etc., which are required to operate at extremely high temperatures, i. e., above about 400 F., as, for instance, 500 F., 1000 F., or higher. When conventional lubricating oils or greases are subjected to such hot operating conditions, decomposition of the petroleum ingredient eventually occurs, with the formation of end products which are hard, abrasive, carbonaceous or coke-like materials which reduce clearance between rubbing members and tend to promote wear.

Broadly, this invention comprises a method of lubricating metal surfaces which in the absence of a lubricant would move in contact with each other at temperatures above about 400 F., by applying to said contacting surfaces a lubricant comprising a major proportion of a volatile solvent such as a light hydrocarbon oil, having a final boiling point below 750 F. and having a viscosity below about 45 seconds Saybolt at 100 F., said oil containing dissolved therein a thickener such as a viscosity-increasing saturated linear aliphatic oxygen-containing polymer having a molecular weight above about 800 and having the property, when heated to high temperature, e, g. above 400 F., of depolymerizing without formation of tar and coke, the amount of'said polymer being sufiicient to make a solution having a viscosity of at least 100 seconds Saybolt at 100 F.

According to another aspect of the invention, there may also be added to the lubricants described above a small amount of a non-abrasive solid which is non-combustible at temperatures up to 2500 F., the particles of which have a smooth surface suitable for solid lubrication. Such materials include graphite, mica, etc., the preferred substance being colloidal graphite, because it is substantially pure, i. e., containing not more than about 0.02% of ash. This colloidal graphite is preferably added in the form of a suspension in a light hydrocarbon liquid such as a light lubricating oil having a Saybolt viscosity of about 75 to 100 seconds at 100 F., or even lighter hydrocarbon vehicles such as refined kerosene or naphtha. A suitable material which is'available commercially contains about 10% of colloidal graphite and of a light lubricating oil such as indicated above.

The low boiling solvent, preferably a hydrocarbon oil, which constitutes the major proportion (usually more than 60%) of the lubricant of this invention, should be below the lubricating oil boiling range, It may be a mineral seal oil which has a boiling range of about 510 to 670 F. or a kerosene which has a boiling range of about 3'75 to 510 F., or various refined naphthas, e. g., those having boiling ranges such as from 300 to 380 F., 220 to 310 F., 160 to 230 F., or even still lower boiling such as to 210 F. The primary purpose of using such a low-boiling oil is that it evaporates at high temperature without formation of varnish or tar, or eventual carbonization.

As the viscosity-increasing polymer, one may use high molecular weight oxygen-containing viscosity-increasing linear aliphatic polymers,preferably having a molecular weight of at least 1,000. Such oxygen-containing thickener is preferably a high molecular weight polymer of an oxygen-containing compound having the group -CI=CH2 in its molecular structure. Such additives include polymers of vinyl ethers having the general formula R2 HQO=JJO-R, in which R1 is an unsubstituted or substituted aliphatic, aromatic, or hydroaromatic radical, and R2 is a hydrogen atom or a substituted or unsubstituted aliphatic radical, e. g., vinyl oleyl ether, vinyl isobutenyl ether, vinyl meta-cresyl ether, vinyl cyclohexyl ether, vinyl octadecyl ether, vinyl chloroethyl ether, vinyl amino propyl ether,

a-ethylvinyl isohexyl ether, a-chloromethyl vinyl 'lauryl ether, etc.; polymers of vinyl esters having the general formula (CH2 CR2'OOC)11Rl, in

which R1 and R2 are as above and n is an integer having a value of 1 or more, e. g., vinyl stearate, vinyl ester of acids obtained by oxidation of paraffin wax, vinyl chloropropionate, vinyl aminopalmitate, vinyl adipate, vinyl citrate, etc.; poly- 'mers of acrylic acid esters having the general formula, ROOC-C(X) =CH2, in which R is an functional group which amylphenyl methacrylate, isoheptyl cyclohexyl chloroacrylate, chlorodecyl methacrylate, etc., especially such polyacrylic esters having a molecular weight of 5,000 to 10,000.

Another case of high molecular weight, oxygencontaining substances which can be used for the purposes of this invention is the class of condensation products or polyesters of substituted fatty acids having the general formula,

in which R is a H atom or an unsubstituted or substituted aliphatic, aromatic, or hydroaromatic group, a: and y may equal or any integer pro-' vided that 'x+y equals at least 5, and where n is 0 or an integer and m is a whole number and Z is a has one replaceable hydrogen atom, Z being capable of esterifyin a carboxyl group. Some of these polyesters are described in U. S. Patent 2,147,647, and are typified by the polyester having a molecular weight of about 14,000 obtained by polyesterification of 12- .hydroxy stearic acid in the presence of a small amount of adipic acid.

The amount of such polymer to be used will depend upon a number of factors such as the type and molecular weight of the polymer, the desired viscosity of the finished lubricant and the conditions under which the lubricant is to be used.

Inasmuch as the thickening effect of the polymer is directly proportional to the molecular weight, a solution having any desired viscosity can be prepared by using a large amount of low molecular weight polymer or a small amount of high molecular weight polymer or various combinations in between. Also, since there is a tendency for the relatively lower molecular weight polymers, i. e., those having a molecular weight of about 800 to 15,000 or so, to be more heat-stable than those of a much higher molecular weight, e. g., 60,000 or 80,000, etc., it may be preferable for some purposes, i. e., where long lubricating life is desired, to use a polymer in the lower range mentioned; whereas for other purposes it may be desirable, i. e., where a short lubricating life is suflicient, perhaps because the supply may be renewed frequently and easily, to use a polymer within the higher range 'of molecular weight. Some examples are: (a) a 20%-solution of a polymer having a molecular weight of 5,000; (b) a 2%-solution of polymer having a molecular weight of 150,000; (0) a 5%-solution of polymer having a molecular weight of about 60,000. Under some circumstances it may be desirable to use a. mixture of low, medium, or high molecular weight, as for instance a mineral seal oil containing dissolved therein 2% of polymer having an average molecular weight of about 150,000 (in order to get a large increase in viscosity with a small amount of addition agent, even though the break-down in molecular weight of this polymer may be fairly rapid), and also containing dissolved therein about by weight of a polymer having an average molecular weight of about 5,000, which, owing to the relatively greater heat stability of this polymer, will extend the life of this lubricating composition over a longer period of time at the high temperature involved. In general, the arithmetic product of per cent of polymer times molecular weight of polymer should be at least 50,000 (per cent molecular weight).

In carrying out the invention, it is apparent from the above discussion of polymers of various molecular weights, that the amount of the polymer to be used may vary over a fairly wide range,

from about 0.3% to about 50% by weight. If colloidal graphite or other solid lubricant is added, the amount thereof to be used should ordinarily be about .052.0% by weight based on the total lubricating composition; preferably the amount of graphite should be about 0.1-0.3%. If the colloidal graphite is added in the form of a suspension in a light oil, as for instance a 10% suspension in oil, the amount of the supension to be used will be about 0.5-20.0%.

If desired, small amounts of otheraddition agents may be added to the lubricating composition, as for instance 0.1 to 2 or 3% of an ester, as for example the low molecular weight alkyl ester of a fatty acid, having the property of increasing the oiliness or lubricity of the composition. Small amounts of other materials such as oxidation inhibitors, depolymerization inhibitors, extreme pressure lubricating agents, etc,

may be added.

Without intending to limit the invention to the particular materials used nor to the proportions in which they were used, the following account is given of a number of industrial applications of this invention. In these tests the mineral seal oil used had a boiling range of about BIO-665 E, and the polymer had an average molecular Weight of about 60,000.

The graphite suspension used contains about 10% colloidal graphite and 90% of a light lubrieating oil having a viscosity of about 75-100 seconds Saybolt at 100 F., and the ester, used in some instances, was an isopropyl ester of wax oxidation acids.

The various compositions used are shown in the following table, which also indicates in certain tests the approximate temperature to which the 4o lubricant was exposed.

Table I Example No 1 2 3 4 5 Composition;

Polymer. per cenL. 7.5 4.3 15 1.7 7.9 Col oidal Graphite Suspension per cent.. 5.0 2.0 3 2.0 2.0 Ester d 1.0 1.0 1.0 Mineral Seal OiL. .5 .1 Temp. of Use 00 Method of Application il Can Oil Cup Mechanical Lubricator a:

All of the above compositions were found satisfactory, some of them being used for the lubrication of-annealing oven car wheel bearings, oven conveyor chains, and kiln car roller bearings, bearings of motor-gear sets subjected to radiant heat of hot metal (as hot as 1100 F.), and bearings of elevators and conveyors handling hot coke.

' In these various industrial uses, great diniculty had previously been experienced in lubrieating the equipment but the compositions of this invention gave excellent results. In a number of cases, after use for a considerable time with these new lubricating compositions, the equipment was disassembled in order to examine the bearings, and invariably the latter showed no signs of carbonaceous deposits and only a thin film of colloidal graphite. An additional practical advantage of this invention is illustrated in the case of test No. 4 where the annealing oven conveyor now rolls readily by gravity, whereas formerly (with previous lubricants) men had difficulty pushing the articles being conveyed on this conveyor. Other were made using lubricants consisting entirely of mineral seal oil and polymer, i. e., without any colloidal graphite or other non-combustible solid materials. Typical of such applications are the lubrication of oven conveyor bearings operating at 420 F., with oil cup application where a blend of 15% polymer, 85% mineral seal oil was utilized; the same lubricant successfully operated on electric motor bearings at temperatures so high that it had previously been impossible to keep even high temperature soda base greases in the bearing housing. Lubrication of ejector pins and other moving hot parts of diecasting machines has been most successful with a blend of 7.5% polymer, 1% ester, 91.5% mineral seal oil. All of these applications are being much more successfully lubricated than with any other previously used lubricants, and show that for certain types of uses the graphite not only may be, but should be, omitted from the composition.

Since the viscosity of the solution of polymer in mineral seal oil is an important factor in obtaining the proper feedin of the lubricant to suit the various types of lubrication means, used in industry, such as referred to at the bottom of the above table, or even by hand where a thick plastic lubricant is used, the following table is given in order to show the effect of the percentage of polymer used, on the viscosity of the mineral seal oil. (The polymer used here was a polymer having an average molecular weight of about 60,000).

Table II Viscosity (Seconds Saybolt at 100 F.) of Mineral Seal Oil Solution Percent of Polymer 925. Plastic Mass.

1 Must be hand-packed.

spect over prior art lubricants i readily demonstrated by the following simple tests:

Example 6 A 10%blend of a lauryl alpha methacrylate.

polymer of about 10,000 average molecular weight, mixed in about 20% concentration with a mineral lubricating oil base stock, was made in mineral seal oil and the blend was heated in a nickel container to about 550 F -until no further change in weight occurred. The residue weighed only .03% of the original blend. This trace was so negligible that obviously no appreciable amount of residue remained. This illustrates the ability industrial applications of the acrylate polymer to decompose without leaving harmful carbonaceous residue.

Example 7 A'polymer similar to that used in Example 6 was added in increasing amounts to a mineral seal oil having a viscosity of about 40 seconds Saybolt at 100 F. until the viscosity of the solution was 100 seconds at 100 F.; about 8% of the polymer was required.

Example 8 Similarly about 5% of polylauryl alpha methacrylate having a molecular weight of about 16,000 is required to raise the viscosity of mineral seal oil from 40 to 100 seconds at 100 F.

Example 9 v a l A light colored tough, rubbery polyester of 12- hydroxy stearic acid, having a molecular weight of about 14,000 was blended in increasing amounts to mineral seal oil until the viscosity was raised from 40 to 100 seconds at 100 F.; about 5% of the polymer was required.

Example 10 A suitable formula containing graphite together with an oxygen-containing polymer is as follows:

Percent by weight Polylauryl alpha methacrylate (about 10,000

mol. wt.) 10

Colloidal graphite 1 Mineral seal oil 88 Total 100 Example 12 The use of these improved oil compositions produces an improved finish on the surface of the metal. For example, the cold rolling of steel, brass, aluminum, copper, or the like is benefited to a great extend by having a film of high temperature lubricant made according to this invention between the rolls and the metal sheet, or other article being rolled. The oil tends to make the surface of the shaped article smoother, to prevent overheating, and to avoid the picking up of particles by the rolls from the material being worked. Similar functions are performed by the oil in metal drawing and die pressing and die forging operations. Although there has been considerable difficulty in the removal of decomposition products of the oils used heretofore for such purposes,

' from the processed articles after they have, been annealed at high temperatures ranging up to about 1750 F., the high temperature lubricant oils of the present invention have all of the advantages of facilitating the fabrication of the metal and improving the surface finish of the metal article being fabricated,,without any disadvantageous staining of the processed articles by dark decomposition products of the lubricant.

For such metal fabricating purposes, the high temperature lubricant of this invention should have a viscosity lying within a considerably narrower range than was indicated above as suitable for lubrication of oven conveyor chains, wheel bearings of annealing oven cars, etc. For instance, for use as a non-staining metal fabricating oil, the finished composition should have a viscosity generally falling within the range of about 55 to about 300 seconds Saybolt at 100 F. The volatile oil base stock should in general boil within the approximate limits of about 300 F. to 750 F.; for instance, a mineral seal oil may be used which has a boiling range of about 510 to 670 F., or a slightly narrower range of 450 F. to 620 F., or a kerosene fraction boiling from 350 to 600 F, may be used, or even a heavy naphtha fraction boiling from 300 to 500 F. may be used. The amount of oxygen-containing polymer to be used as thickener, will of course depend upon the viscosity of the volatil oil base stock and upon the viscosity desired in the finished lubricant, as well as upon the type and'molecular weight 01 the polymer, as indicated above.

Also, for such metal fabricating purposes, it is frequently desirable to add to the lubricant a small amount of an oiliness agent (about 0.1% to 2% or 3% by weight), such as a fatty ester, a fatty oil, a vegetable oil, a soap, or certain other oiliness agents such as tricresyl phosphate, and the like.

A suitable composition for use as a non-staining metal fabrication oil is as follows:

Percent by weight Mineral seal oil (boiling from about 500- 600 F.) 96 Polylauryl alphamethacrylate (about 10,000 mol. wt.) Isopropyl esters of oxidized wax acids 1 Total 100 It is indeed very surprising that high molecular weight oxygen-containing polymers can be decomposed at high temperature without leaving any substantial undesirable decomposition residue, and this is believed particularly remarkable in the case of the acrylic acid ester polymers, because it was expected that such materials would result in a large amount of charring and undesirable carbonaceous residue if heated to a decomposition temperature.

Although the theory of the mechanism of the operation of the invention is not entirely understood, it is believed to depend partly upon the use of an operating temperature sufficiently high to cause at least partial depolymerization or the polymer, such as at least 500 F. or preferably 550 F. or higher. Conversely, it is believed that the polymer or thickening agent should be one which decomposes, by depolymerization or otherwise, when subjeoted to operating temperatures involved, and does so without leaving any substantial amount of carbonaceous residue. Furthermore, the mineral seal oil or other even more volatile solvent, which appears to be necessary primarily as a vehicle or fluid medium for getting the polymer, alone or with the graphite, into place in the bearing, should be a liquid which evaporates under the operating temperatures involved, without leaving any carbonaceous, varnish-like or tarry residue, which would either undesirably increase the resistance. of the moving metal parts or would cause harmful abrasion thereof.

This application is a continuation-in-part of application Serial No. 366,714, filed November 22, 1940, now Patent No. 2,356,367, issued August 22, 1944. It is not intended that the invention be limited to any of the materials which have been mentioned merely as specific examples, nor by the specific proportions given for the sake of illustration, nor by any theory as to the mechanism of the invention, but only by the appended claims in which it is intended to claim all novelty inherent in the invention as broadly as the prior art permits.

I claim:

1. The method of lubricating hot metal surfaces which, in the absence of a lubricant, would move in contact with each other, at temperatures above about 500 R, which comprises applying to said moving metal parts a lubricant comprising a major proportion of a volatile hydrocarbon solvent having a boiling range within F. and F. having a viscosity below 45 seconds Saybolt at 100 F. and capable of evaporating at such high temperatures without leaving any harmful residue, said lubricant also containing a sufilcient amount of an oil-soluble organic thickener comprising essentially a substantially saturated oxygen-containing viscosity-increasing linear aliphatic polymer having a molecular weight of at least 1,000, adapted to be decomposed at such high temperatures without leaving any substantially harmful residue, to make a solution having a viscosity of at least 100 seconds Saybolt at 100 F., and said thickener being a polymer of an oxygen-containing compound having the group (IJ=CH2 in its molecular structure.

2. The method of lubricating metal surfaces at a temperature above 500 F. which comprises applying to said moving metal parts a lubricant consisting essentially of mineral seal oil and an acrylic acid ester polymer of at least 1,000 molecular weight, the amount of that polymer being sufficient to make a solution having a viscosity of at least about 100 seconds Saybolt at 100 F.

3. The method of lubricating metal surfaces at temperatures above about 500 F. which comprises applying to said moving metal parts a lubricant comprising a major proportion of a hydrocarbon oil having a final boiling point below about 675 F. and having a viscosity below about 45 seconds Saybolt at 100 F., said lubricant also containing dissolved therein a sufiicient amount of a substantially saturated acrylic acid ester polymer having a molecular weight of at least 1,000 to make a hydrocarbon solution having a viscosity above 100 seconds Saybolt at 100 F., the prod- ,uct of the per cent of polymer times the molecular weight of the polymer being at least 50,000, and said lubricant also containing a small amount of a non-abrasive solid lubricant which is noncombustible at temperatures up to about 2500 F.

4. The method of lubricating hot metal surfaces which, in the absence of a lubricant, would move in contact with each other at temperatures above about 500 F., which comprises applying to said moving metal parts a lubricant consisting essentially of a major proportion of mineral seal oil, about 0.3 %-20% of polylauryl alpha methacrylate having an average molecular weight of about 5,000 to 20,000, the amount of said polymer being sufficient to make a mineral oil solution having a viscosity of at least 100 seconds Saybolt at 100 F., the product of the per cent of polymer 9 times the molecular weight of the polymer being at least 50,000, said lubricant also containing about .05% to 2.0% of colloidal graphite.

5. A high temperature lubricant for lubrication of moving metal parts at temperatures above about 500 E, which comprises at least 60% by weight of mineral seal oil, about 0.3-20% of polylauryl alpha methacrylate having an average molecular weight of about 5,00020,000, the amount of said polymer being sufflcient to make a. mineral oil solution having a viscosity of at least 100 seconds Saybolt at 100 F., said lubricant also containing about .05 %2.0% of colloidal graphite.

DONALD L. WRIGHT.

REFERENCES CITED The following references are of record in thefile of this patent:

Number Davis Nov. 23, 1943 

